The present invention relates to a solid-state or charge-coupled image sensor.
According to the prior art method for fabricating solid-state image sensors, prior to the formation of CCD gate electrodes and overflow control gates, overflow drains are formed by the dopant introduction step such as an ion-implantation or thermal diffusion step. Therefore, due to accumulated dimensional variations which in turn are due to manufacturing tolerances in lithographic steps the overflow control gates and overflow drains are misaligned and they are very frequently overlapped. As a consequence, the channel length varies from one overflow control gate to another and consequently a saturation charge varies from one photodiode to another. Therefore, even when the image sensor is uniformly exposed, a photodiode in a charge-coupled unit cell whose overflow-control-gate channel length is shorter is saturated faster. As a result, the luminous intensity varies from one spot to another on a cathode-ray tube.